Viability of preserved Cryptosporidium baileyi oocysts

Abstract

The present study was undertaken to determine the viability and infectivity of oocysts of Cryptosporidiumbaileyi that had been stored from 1 to 40 months at 4?C preserved in 2.5% potassium dichromate solution. Oocysts ofC. baileyi were purified from the feces of experimentally infected chickens using discontinuous sucrose gradients.Subsequently, the purified oocysts were suspended in 2.5% potassium dichromate solution at a concentration of 1 ×107 organism/ml, and their viabilities were assessed by nucleic acid staining, histologic examination, and infectivity to2-day-old chickens. All chickens inoculated with oocysts that had been stored for 1-18 months developed patentinfections, while chickens infected with older oocysts remained uninfected. Between 5.8% and 82.2% of the oocysts,stored at 4?C in 2.5% potassium dichromate solution, were found to be viable, as determined by nucleic acid staining.Parasite colonization in the bursa of Fabricius was detected in the microvillus border of bursal epithelium. The findingthat C. baileyioocysts remain infective to chickens for at least 18 months offers important time-saving advantages toinvestigators who frequently require large numbers of oocysts.